1. Field of the Invention
The invention relates to safety means for a fluid operated tool of the type having firing control means comprising two separate and independent triggering means and requiring both triggering means to be concurrently in their firing positions to actuate the tool. More particularly, the invention relates to safety means introducing into the firing sequence of the firing control means a time limit within which both triggering means must achieve their firing positions.
2. Description of the Prior Art
The safety means of the present invention is applicable to any fluid operated tool of the type having two separate and independent triggering means, both of which must concurrently be in their firing positions to enable actuation of the tool. The invention is readily applicable, for example, to pneumatic fastener applying devices such as stapling tools or nailing tools. While not intended to be so limited, for purposes of an exemplary showing the safety means of the present invention will be described in terms of its application to a pneumatic fastener applying device of the general type set forth in U.S. Pat. No. 3,170,487. The tool may be provided with any appropriate separate and independent triggering means. Again, for purposes of an exemplary showing, the tool will be described as having separate triggering means similar to those set forth in U.S. Pat. No. 3,278,106.
In recent years, prior art workers have been continuously developing fastener applying devices capable of driving larger and larger fastener elements and characterized by increased speeds of operation. Along with the increased capabilities of these fastener applying devices have come increased safety hazards, it being understood that a fastener applying device with sufficient power to drive a large fastener element is at the same time capable of firing the fastener element a considerable distance through the air with the resultant possibility of injury.
To overcome these hazards, prior art workers have devised a number of safety devices. Primary among these was the firing control means having two separate and independent triggering means, both of which must be concurrently in their firing positions to actuate the fastener applying tool. The separate and independent triggering means for fastener applying tools are generally in the form of a manual trigger and a workpiece responsive trip.
The above mentioned U.S. Pat. No. 3,278,106 taught independent triggering means shiftable to their firing positions in any order, materially increasing the rate of operation of the tool while maintaining the safety advantage of the dual triggering means system.
However, a hazard still arises when a tool of the type taught in U.S. Pat. No. 3,278,106 is carried around with the manual trigger in its firing position. Anything brushing against the workpiece responsive trip with sufficient force to shift it to its firing position will fire a fastener into the brushing object, whether it be animate or inanimate. If the manual trigger is unintentionally shifted to its firing position or held in its firing position by the operator, which action may be subconscious, and if the workpiece responsive trip is brushed with sufficient force against a portion of the operator's body, and undesired portion of the workpiece or any other element, a fastener may be fired. If a fastener is unintentionally driven against a hard, tough or brittle element, the fastener may ricohet or scatter fragments of the element at high speed.
The safety means of the present invention greatly reduces these hazards through the basic concept of providing a time limit within which both separate and independent triggering means must reach their firing positions to enable operation of the tool. The independent triggering means may be shifted to their firing positions in any order, but if they are not concurrently in their firing positions within the required time limit a lock-out device is actuated which prevents firing of the tool. If the lock-out device is activated, it can only be deactivated by the return of a selected one or both of the triggering means to their normal positions.
The functions of the safety means of the present invention can be embodied in a number of different ways such as through the use of cam means, levers or linkages, various combinations of valves, combinations of valves and mechanical linkages, moving or non-moving part fluidic devices or such devices in combination with valves, linkages and the like. The various elements used to implement the safety means of the present invention may be actuated pneumatically, mechanically, magnetically or by other appropriate means. Similarly, the lock-out device may take any appropriate form and may prevent firing of the tool through any suitable means.
The lock-out device prevents firing of the tool after the expiration of the time limit imposed by the safety means of the present invention. The time limit may be initiated by the manual trigger and not the workpiece responsive trip; by the workpiece responsive trip and not by the manual trigger; or, in a preferred embodiment, by that one of the manual trigger and the workpiece responsive trip which is shifted to its firing position first. Actuation of the other previously released triggering means so that both triggering means are in the firing position within the time limit, will fire the tool. Actuation of the other previously released triggering means after the time limit, so that both triggering means are not concurrently in their firing positions within the time limit, will not fire the tool. The time limit is reset by releasing the manual trigger (if the trigger only starts the time limit), by release of the workpiece responsive trip (if the trip only starts the time limit), or by releasing both the manual trigger and the workpiece responsive trip (if either triggering means will initiate the time limit).
The time limit is reset each time the tool is fired by other means independently operated by the firing mechanism. This permits firing of the tool as long as one of the triggering means is in its firing position and the other of the triggering means is shifted to its firing position in rapid sequence separated by intervals shorter than the time limit interval.
In an instance where the manual trigger only initiates the time limit, protection would be achieved against damage or injury from unintentionally brushing the workpiece responsive trip against some object. In an instance where only the workpiece responsive trip initiates the time limit, protection would be gained against mislocated fasteners in the work during rest or idle periods. In the preferred embodiment wherein both triggering means can initiate the time limit, protection against both types of hazards can be achieved. In any embodiment, the time limit should be of such duration that the tool can only be fired unintentionally only with great difficulty.